Cart Promo Rules

Promo rules (shopping cart price rules) are applied via the Totals framework, registered in Magento/SalesRule/etc/sales.xml. They follow the same engine as Catalog Price Rules but add coupon code support.

Conditions define a boolean function that determines if a rule applies to a cart. Conditions support:

• Cart subtotal, quantity, weight, etc.
• EAV attributes of products in the cart (e.g., category, custom attributes).
• Customer segments (when enabled).

Further reading: StackExchange: Shopping Cart Rule Based on Custom Attribute

Four action types define how discounts apply:

1. Percent of product price discount
   • Subtracts a percentage from each qualifying item's price.
   • Example: Discount Amount = 10 → 10% off each item.
2. Fixed amount discount
   • Subtracts a fixed amount from each qualifying item's price.
   • Example: Discount Amount = 10 → $10 off each item.
3. Fixed amount discount for whole cart
   • Subtracts a fixed amount from the cart total (usually subtotal).
   • Example: Discount Amount = 10 → $10 off cart subtotal.
   • Optional: Apply to shipping as well ("Apply to Shipping Amount").
4. Buy X get Y free
   • Defines a quantity X the customer must purchase to receive quantity Y for free.
   • Discount Amount represents Y (free quantity).

Unlike catalog price rules, cart promo rules can require coupon codes. Coupons can be:

• Specific: Defined codes (e.g., "SUMMER20").
• Auto-generated: Magento generates codes with a pattern/prefix.
• No coupon: Rule auto-applies when conditions match.

A promo rule can be configured to:

• Discount shipping: Apply to Shipping Amount option.
• Free shipping: Special action that sets shipping cost to zero.

Tax calculation settings affect discount application. Subtleties include:

• Before/after discount: Taxes can be calculated before or after discount is applied.
• Including/excluding tax: Configuration determines if discounts apply to tax-inclusive or tax-exclusive amounts.

See admin: Stores → Configuration → Sales → Tax → Calculation Settings.

Both promo rules and catalog price rules use the same Rule engine for conditions. Main difference: cart promo rules support coupons and apply at cart/checkout scope, while catalog rules apply at product listing scope.

• Cart Price Rules (Official Docs)
• StackExchange: Shopping Cart Rule Based on Custom Attribute
• Module Reference: Magento_SalesRule